This invention relates to a recording/reproducing method of optical information, wherein a light flux emitted from a light source is converged on an information recording plane and optical information to be reproduced is recorded on an optical information recording medium, or information on the information recording plane is reproduced, to an optical pickup apparatus, to a converging optical system, an objective lens to be used therefor, and to a recording/reproducing apparatus for optical information recording medium.
In recent years, with the practical use of a red semiconductor laser of a short wavelength, development of a DVD (digital video disk or called also a digital versatile disk), which is a high-density optical information recording medium having a larger capacity but a size of the same degree as a CD (compact disk) which is a conventional optical information recording medium (also called an optical disk), has been promoted. In this DVD, the numerical aperture NA of the objective lens at the side of the optical disk is made to be 0.6 in the case where a short wavelength semiconductor laser of 635 nm is used. Further, a DVD has a track pitch of 0.74 xcexcm and a minimum pit length of 0.4 xcexcm, and is made to have a high density more than twice in comparison with a CD, which has a track pitch of 1.6 xcexcm and a minimum pit length of 0.83 xcexcm. Moreover, in addition to the above-mentioned CD and DVD, optical disks having various standards, for instance, such as a CD-R (a direct read after write, writing once compact disk), a CD-RW, an LD, an MD (mini-disk), a DVD-RAM and an MO (magneto-optic disk) are merchandised and have come into general use. In Table 1, the thickness of the transparent substrate and the required numerical aperture of various optical disks are shown.
Besides, with regard to the CD-R, it is necessary for the light source to have a wavelength xcex=780 (nm), but for the other optical disks, a light source having a wavelength other than those noted in Table 1 can be used; in this case, the required numerical aperture NA should be varied in accordance with the wavelength xcex of the light source used. For example, in the case of a CD, the required numerical aperture is approximated by NA=xcexc (xcexcm)/1.73, and in the case of a DVD, it is approximated by NA=xcex (xcexcm)/1.06.
Further, the numerical aperture as referred to in this specification (for example, referred to as NA1, NA2, NAL, NAH, NA3, NA4, etc. hereinafter) means the numerical aperture of the converging optical system as seen from the transparent substrate side. NA1 is a numeral aperture necessary for reproducing information from or recording information in the first optical information recording medium and NA2 is a numeral aperture necessary for reproducing information from or recording information in the second optical information recording medium.
As described in the above, it is now an age when various kinds of optical disks, which are different in the size, the thickness of the transparent substrate, the recording density, the wavelength used, and so forth, are available on the market, and optical pickup apparatus capable of being used for various kinds of optical disks are proposed.
As one of them, it has been proposed an optical pickup apparatus which is equipped with converging optical systems corresponding to the different optical disks respectively, and the converging optical systems are switched over in accordance with the optical disk to be reproduced. However, in this optical pickup apparatus, a plurality of converging optical systems is required and it brings not only a high cost but also the necessity of a driving mechanism for switching over the converging optical systems; accordingly, the device is not desirable because of the complexity and the requirement of the precision in switching over.
Therefore, various kinds of optical pickup apparatus which can reproduce a plurality of optical disks by using a single converging optical system.
Incidentally, in this specification, the phrase xe2x80x98to reproduce an optical diskxe2x80x99, xe2x80x98to record an optical diskxe2x80x99 or the like is used in the sense xe2x80x98to reproduce information in an optical disk, xe2x80x98to record information in an optical diskxe2x80x99, or the like for simplicity""s sake.
As one of them, in Japanese laid open patent H7-302437, an optical pickup apparatus, wherein the refracting surface of the objective lens is divided into a plurality of ring-shaped domain, and each of the divisional surface domains makes the beam converge on one of the optical disks having different thickness to reproduce information, is described.
Besides, in Japanese laid open patent H7-57271, an optical pickup apparatus, wherein, in the case of the first optical disk with the thickness of the transparent substrate t1, an objective lens designed to make the wave front aberration included in the converged beam not larger than 0.07xcex is employed, and in the case of the second optical disk having the thickness of the transparent substrate t2, the converged beam spot is formed in a little defocused state, is described.
However, in the optical pickup apparatus described in Japanese laid open patent H7-302437, it is necessary to make the laser output large because the incident light quantity is simultaneously divided into two focal points by a single objective lens, which brings about high cost. Further, in the optical pickup apparatus described in Japanese laid open patent H7-57271, increasing of jitter owing to side lobe occurs when the reproduction of the second disk is carried out. In particular, because the second disk is subjected to reproduction forcibly by the objective lens which makes the wave front aberration not larger than 0.07xcex for the first optical disk, there is a limit in the numerical aperture capable of reproducing the second optical disk.
With the background stated above, there are given methods proposed to solve the above-mentioned problems, which are disclosed in Japanese TOKKAIHEI Nos. 8-55363, 9-17023, 9-194975, 10-69675 and 11-96585.
However, when recording information on an optical information recording medium, another problem is further caused. In general, greater laser power is required for recording on an optical information recording medium than for reproducing, and this difference of power changes a wavelength of a light source (which is also called wavelength shift or wavelength drift), thus, chromatic aberration based on the wavelength change is caused. When chromatic aberration of an optical system is not corrected, a light converging position is changed by the wavelength shift, and a focal point is shifted, resulting in possibility of occurrence of an error in recording and/or reproducing of information.
For solving problems caused by wavelength changes, there have been proposed various optical systems each having a function of correcting chromatic aberration. However, none of them is one wherein reproducing/recording of plural optical information recording media can be conducted by one converging optical system.
In other words, in the prior art, it has been impossible to obtain an objective lens, an optical pickup apparatus and an optical information recording/reproducing apparatus wherein one converging optical system (with one or plural light sources) can cope with recording/reproducing of various optical disks each having different size, board thickness, recording density and wavelength to be used, a problem of chromatic aberration caused by wavelength shift derived from change of power in recording is solved, and thereby, recording/reproducing can be conducted satisfactorily.
An object of the invention is to solve the problems stated above and to provide an objective lens, an optical pickup apparatus and an optical information recording/reproducing apparatus wherein one converging optical system (with one or plural light sources) can cope with recording/reproducing of various optical disks each having different size, board thickness, recording density and wavelength to be used, a problem of chromatic aberration caused by wavelength shift derived from change of power in recording is solved, and thereby, recording/reproducing can be conducted satisfactorily.
The above-mentioned objects can be attained by either one of the following structures.
An optical pickup apparatus for reproducing information from one of different kinds of optical information recording medium, each having a transparent substrate in different thickness, or for recording information onto one of said different kinds of optical information recording medium, comprising: a light source for emitting light flux; a converging optical system having an optical axis, a ring-zonal diffraction section, and a refracting surface including a first portion, a second portion and a third portion, wherein the third portion is farther from the optical axis than the first portion, and the second portion is provided between the first portion and the third portion; and an image sensor, wherein the first portion and the third portion are capable of converging the light flux on a first information recording plane of a first optical information recording medium having a first transparent substrate of thickness t1, to reproduce information recorded in the first optical information recording medium, wherein the first portion and the second portion are capable of converging the light flux on a second information recording plane of a second optical information recording medium having a second transparent substrate of thickness t2, to reproduce information recorded in the second optical information recording medium, wherein t2 is greater than t1, and wherein the image sensor is capable of receiving light flux reflected from the first information recording plane or the second information recording plane.
The optical pickup apparatus according to Structure 1 wherein when A represents an amount of focal point shifting caused on the above-mentioned refracting surface by a wavelength change of a light flux emitted from the light source, and B represents an amount of focal point shifting caused on the above-mentioned ring-zonal diffraction section by a wavelength change of a light flux emitted from the light source, the following conditional expression is satisfied.
0 less than =|A+B| less than =|A|
The optical pickup apparatus according to Structure 2, wherein the following conditional expression is satisfied.
|A+B|=0
The optical pickup apparatus according to Structure 2, wherein the wavelength of a light flux emitted from the light source is changed based on the change in an amount of electric current supplied to the light source.
The optical pickup apparatus according to Structure 2, wherein the optical pickup apparatus has therein the aforesaid light source (first light source) and a second light source which emits a light flux whose wavelength is longer than that emitted from the first light source, and the conditional expression above is satisfied for the light flux emitted from the first light source.
The optical pickup apparatus according to Structure 1, wherein the converging optical system has an objective lens which further has therein the optical axis, the refracting surface (including the first divisional portion, the second divisional portion and the third divisional portion) and the ring-zonal diffraction section, and the ring-zonal diffraction section is provided on the surface of the objective lens which is opposite to the refracting surface.
The optical pickup apparatus according to Structure 6, wherein the ring-zonal diffraction section is provided on the mostly entire portion of the surface which is opposite to the refracting surface.
The optical pickup apparatus according to Structure 1, wherein the converging optical system has an objective lens which further has therein the optical axis, the refracting surface (including the first divisional portion, the second divisional portion and the third divisional portion) and the ring-zonal diffraction section, and the ring-zonal diffraction section is provided on the refracting surface.
The optical pickup apparatus according to Structure 8, wherein the ring-zonal diffraction section is provided also on each of the first divisional portion, the second divisional portion and the third divisional portion of the refracting surface.
The optical pickup apparatus according to Structure 1, wherein the converging optical system has an objective lens which further has therein the optical axis and the refracting surface (including the first divisional portion, the second divisional portion and the third divisional portion), and the ring-zonal diffraction section is provided on an optical member which is different from the objective lens.
The optical pickup apparatus according to Structure 2, wherein an amount of change in wavelength of a light flux emitted from the light source is xc2x120 nm or less.
An objective lens having an aspherical face for use in an optical pickup apparatus for reproducing information from one of different kinds of optical information recording medium, each having a transparent substrate in different thickness, or for recording information onto one of said different kinds of optical information recording medium, lens comprising: a ring-zonal diffraction section; and an optical surface having a first divided surface, a second divided surface, and a third divided surface, wherein the third divided surface is farther from the optical axis than the first divided surface, the second divided surface is provided between the first divided surface and the third divided surface, wherein the objective lens is capable of converging a first light flux which passes through the first divided surface and a third light flux which passes through the third divided surface on a first information recording plane of a first optical information recording medium through a first transparent substrate of the first optical information recording medium, to reproduce information recorded in the first optical information recording medium, the thickness of the first transparent substrate is t1, and wherein the objective lens is capable of converging the first light flux and a second light flux which passes through the second divided surface on a second information recording plane of a second optical information recording medium through a second transparent substrate of the second optical information recording medium, to reproduce information recorded in the second optical information recording medium, the thickness of the first transparent substrate is t2 which is greater than t1.
The objective lens according to Structure 12 wherein the ring-zonal diffraction section is provided on the surface which is different from the refracting surface.
The objective lens according to Structure 12 wherein the ring-zonal diffraction section is provided on the mostly entire portion of the surface which is different from the refracting surface.
The objective lens according to Structure 12 wherein the ring-zonal diffraction section is provided on the refracting surface.
The objective lens according to Structure 12 wherein the ring-zonal diffraction section is provided also on each of the first divisional portion, the second divisional portion and the third divisional portion of the refracting surface.
The objective lens according to Structure 12 wherein when A represents an amount of focal point shifting caused on the above-mentioned refracting surface by a wavelength change of a light flux emitted from the light source, and B represents an amount of focal point shifting caused on the above-mentioned ring-zonal diffraction section by a wavelength change of a light flux emitted from the light source, the following conditional expression is satisfied.
0 less than =|A+B| less than =|A|
The objective lens according to Structure 12 wherein the following conditional expression is satisfied.
|A+B|=0
An optical information recording medium reproducing or recording apparatus for reproducing information from one of different kinds of optical information recording medium, each having a transparent substrate in different thickness, or for recording information onto one of said different kinds of optical information recording medium, said optical information recording medium reproducing or recording apparatus comprising: an optical pickup apparatus comprising: a light source for emitting light flux; a converging optical system having an optical axis, a ring-zonal diffraction section, and a refracting surface including a first portion, a second portion and a third portion, wherein the third portion is farther from the optical axis than the first portion, and the second portion is provided between the first portion and the third portion; and an image sensor, wherein the first portion and the third portion are capable of converging the light flux on a first information recording plane of a first optical information recording medium having a first transparent substrate of thickness t1, to reproduce information recorded in the first optical information recording medium, wherein the first portion and the second portion are capable of converging the light flux on a second information recording plane of a second optical information recording medium having a second transparent substrate of thickness t2, to reproduce information recorded in the second optical information recording medium, wherein t2 is greater than t1, and wherein the image sensor is capable of receiving light flux reflected from the first information recording plane or the second information recording plane.
The optical information recording medium recording/reproducing apparatus according to Structure 19, wherein when A represents an amount of focal point shifting caused on the above-mentioned refracting surface by a wavelength change of a light flux emitted from the light source, and B represents an amount of focal point shifting caused on the above-mentioned ring-zonal diffraction section by a wavelength change of a light flux emitted from the light source, the following conditional expression is satisfied.
0 less than =|A+B| less than =|A|
The optical information recording medium recording/reproducing apparatus according to Structure 20 wherein the following conditional expression is satisfied.
xe2x80x83|A+B|=0
The optical information recording medium recording/reproducing apparatus according to Structure 19, wherein the converging optical system has an objective lens which further has therein the optical axis, the refracting surface (including the first divisional portion, the second divisional portion and the third divisional portion) and the ring-zonal diffraction section, and the ring-zonal diffraction section is provided on the surface of the objective lens which is opposite to the refracting surface.
The optical information recording medium recording/reproducing apparatus according to Structure 19, wherein the converging optical system has an objective lens which further has therein the optical axis, the refracting surface (including the first divisional portion, the second divisional portion and the third divisional portion) and the ring-zonal diffraction section, and the ring-zonal diffraction section is provided on the refracting surface.
The optical information recording medium recording/reproducing apparatus according to Structure 19, wherein the converging optical system has an objective lens which further has therein the optical axis and the refracting surface (including the first divisional portion, the second divisional portion and the third divisional portion), and the ring-zonal diffraction section is provided on an optical member which is different from the objective lens.
A chromatic-aberration-corrected objective lens for recording and/or reproducing representing an optical system for an optical pickup apparatus which converges a light flux emitted from a light source on an information recording surface with one converging optical system through a transparent substrate, for recording information on and/or reproducing information from the information recording surface, wherein at least one optical surface constituting the converging optical system is made to be a refracting surface which is divided into plural ring zones which are coaxial with the optical surface, and a diffraction ring-zonal lens is provided on at least one other optical surface, to offset chromatic aberration caused on the refracting surface by a wavelength difference by chromatic aberration caused by the diffraction ring-zonal lens.
The chromatic-aberration-corrected objective lens for recording and/or reproducing according to Structure 25 wherein, in the optical system for an optical pickup apparatus in which light fluxes emitted from light sources each being different in terms of wavelength are converged on information recording surfaces by one converging optical system through transparent substrates for recording and/or reproducing information on the information recording surfaces, for the first optical information recording medium having a t1 thick transparent substrate and the second optical information recording medium having a t2 (t2xe2x89xa0t1) thick transparent substrate, at least one optical surface constituting the converging optical system is made to be one which is divided into the first divisional portion located in the vicinity of an optical axis positioned at the center of the optical surface, the third divisional portion and the second divisional portion which is sandwiched between the first and third divisional portions, a beam spot is formed by light fluxes which have passed through the first and third divisional portions, for recording and/or reproducing of the first optical information recording medium having a t1 thick transparent substrate, a beam spot is formed by light fluxes which have passed through the first and second divisional portions, for recording and/or reproducing of the second optical information recording medium having a t2 (t2xe2x89xa0t1) thick transparent substrate, and chromatic aberration caused on the refracting surface and chromatic aberration caused by the diffraction ring-zonal lens both in the case of recording and/or reproducing of the first optical information recording medium having a t1 thick transparent substrate, are made to offset each other.